Large Meteorite Impacts (2003)
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STRUCTURAL INVESTIGATIONS IN THE CENTRAL UPLIFT OF THE UPHEAVAL DOME IMPACT
CRATER, UTAH. D. Scherler1, A. Jahn1 and T. Kenkmann1. 1Institut für Mineralogie, Museum für Naturkunde,
Humboldt-Universität Berlin, Invalidenstrasse 43, D-10115 Berlin, Germany, [email protected].
Introduction: The Upheaval Dome structure is a
morphological expression of variously deformed sedimentary rocks in the otherwise relatively flat lying
rocks of the Colorado Plateau in SE Utah. It has been
identified to be an impact structure by early workers
such as Shoemaker et al. in 1983 [1]. Even though
Jackson et al. [2] proposed a concurring genetic theory
of salt tectonics, geological [3] and geophysical [4]
contributions as well as recent rock mechanical evidence [5] provides us with the impact-theory as the
most favorable starting point for a kinematic model of
the structure’s genesis. Using geological and structural
features, which were mapped during a field campaign
in the innermost part, comprising of layered Triassic
rocks (Chinle & Moenkopi formations), we generated a
3D-model using ArcGIS and the 3D-Analyst by ESRI.
In addition to the mapping, several samples of the outcropping lithologies were taken to compare their microstructure with respect to those of undeformed samples in later work. By combining field observations
with the visualization benefits of a 3D-model, important structural elements, their lateral development and
relevance for uplifting material shall provide helpful
insights on the formation of a central uplift in a layered
target. The spatial distribution of the dipping strata,
faults, folds and cataclastically deformed rocks were
used for imposing constraints on the kinematics of
central uplift formation during crater collapse. The
work is in progress and displayed are the results so far.
Further processing of the data shall result in a structure-map of marker horizons, the 3D-visualization of
faults and eventually a balanced restoration of movements during crater collapse.
Structure and Deformation: The mapped units
mainly consist of terrigenous clastic lithologies and are
dominated by sand- and siltstones. Their deformational
behavior range over a large scale though aren’t everywhere visible due to distributed faulting and weathering. Close spaced fracturing is abundant over the entire
structure and even though only small individual offsets
(mm-cm) can be observed (Fig. 1), their accumulation
might result in remarkably strain on a macroscale. On a
dm- to m-scale, intraformational thrusting in a rampflat-geometry is common in stratified units such as the
Jurassic Kayenta Formation or the Chinle and Moenkopi Formations. While concentric shortening, bound
to reverse faults or folding, is well localized at the perimeter, the fault pattern gets more complex
Fig. 1: Blockview of Church Rock sample (Chinle Fm)
and diffuse towards the center. Anyhow, several major
thrust faults are traceable from the margin of the
mapped area towards the center and allow to distinguish blocks of relatively less internal deformation.
Their radial arrangement [6], likewise reported from
the Spider Impact Structure [7] in an iris-like fashion,
appears to allow the accommodation of vertical displacement by stacking of inward flowing material. The
amount of displacement increases centerward and is
sometimes seen to develop from a radial striking fold,
eventually indicating thrust direction by its vergency.
Clastic dikes [2,3] of different lithologies occur
throughout the structure but concentrate in the center,
where the White Rim Sandstone (Permian), as the lowermost outcropping unit, forms a complex dike network
[7]. It’s proximity to the overlying Hoskinnini Member
suggests short transport distances. Other dike occurrences are generally smaller and the determination of
their protoliths is future work, but can on first sight by
means of color and mineralogy be restricted to highporosity sandstones. In several locations, sandstones of
various lithologies, though not displaced as dikes, display thickening with a massive appearance and the loss
of sedimentary structures.
Rock masses within Wingate Sandstone (~100 m
thick unit overlying the Triassic formations mentioned
above) that outcrop at the perimeter of the inner depression appear to have undergone some ductile deformation similar to the dike rocks. Besides folding,
due to convergent material flow, in some places the
rock became displaced into the hanging wall unit with
dike-like crosscutting relationships. The downward
displacement of these rock masses apparently affected
the internal geometry of the central uplift during its
formation as seen from a normal fault overprint of a
reverse fault structure.
Large Meteorite Impacts (2003)
3D-Model and data processing: The GISdatabase (Fig. 2) consists of a DTM (A), polygons (e.g.
outcropping units, B), lines (e.g. faults, C) and points
(e.g. dips, D). The result is a DTM covered with geological signatures (E). Besides our own mapping of the
innermost part, further information was taken from the
works of [2] and [3].
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Using spatial analytical tools, such as geostatistical
interpolation for generating surface data from point
information, we processed the data, generating thematic maps. Fig. 3 shows a dip-map (interpolation via
kriging), that lines out the spatial variance of dip angles. Since the Kayenta Formation, just inside of the
ring syncline, is a well stratified (and traceable) unit,
distributed intraformational faulting, makes for strong
varying dip-angles that reach high values, and results in
thickening of the unit [6]. Even though a canyon cuts
through the WNW’ perimeter of the structure, there
seems to be some symmetry with low dip-angle sectors
in the WNW and ESE, since comparing dip-angles
with topographic height showed no significant trend.
This spatial variation might reflect an oblique impact
scenario as proposed earlier [6], striking WNW-ESE.
Fig. 3: Dip-map. Inner polygon is the mapped area.
Acknowledgement: This work is funded by the German Science Foundation (DFG), grant KE-732-6.
Fig. 2: Components of 3D-geological model.
References:[1] Shoemaker, E. M., Herkenhoff, K.
E. (1984) LPSC XV, 778-779. [2] Jackson, M. P. A.
et al. (1998) GSA Bulletin, 110(12), 1547-1573.
[3] Kriens, B. J. et al. (1999) JGR, 104(E8), 18,86718,887. [4] Kanbur, Z. et al. (2000) JGR, 105(E5),
9489-9505. [5] Kenkmann, T. (2003) EPSL (submitted). [6] Kenkmann, T., Scherler, D. (2002) LPSC
XXXIII, #1037. [7] Shoemaker, E. M., Shoemaker, C.
S. (1996) AGSO J. Austr. Geol. & Geoph., 16(4), 379398.